Cancer
Cancer is one of the most common diseases, and a major cause of death in the western world. In general, incidence rates increase with age for most forms of cancer. As human populations continue to live longer, due to an increase of the general health status, cancer may affect an increasing number of individuals. The cause of most common cancer types is still largely unknown, although there is an increasing body of knowledge providing a link between environmental factors (dietary, tobacco smoke, UV radiation etc) as well as genetic factors (germ line mutations in “cancer genes” such as p53, APC, BRCA1, XP etc) and the risk for development of cancer.
No definition of cancer is entirely satisfactory from a cell biological point of view, despite the fact that cancer is essentially a cellular disease and defined as a transformed cell population with net cell growth and anti-social behavior. Malignant transformation represents the transition to a malignant phenotype based on irreversible genetic alterations. Although this has not been formally proven, malignant transformation is believed to take place in one cell, from which a subsequently developed tumor originates (the “clonality of cancer” dogma). Carcinogenesis is the process by which cancer is generated and is generally accepted to include multiple events that ultimately lead to growth of a malignant tumor. This multi-step process includes several rate-limiting steps, such as addition of mutations and possibly also epigenetic events, leading to formation of cancer following stages of precancerous proliferation. The stepwise changes involve accumulation of errors (mutations) in vital regulatory pathways that determine cell division, asocial behavior and cell death. Each of these changes may provide a selective Darwinian growth advantage compared to surrounding cells, resulting in a net growth of the tumor cell population. A malignant tumor does not only necessarily consist of the transformed tumor cells themselves but also surrounding normal cells which act as a supportive stroma. This recruited cancer stroma consists of connective tissue, blood vessels and various other normal cells, e.g., inflammatory cells, which act in concert to supply the transformed tumor cells with signals necessary for continued tumor growth.
The most common forms of cancer arise in somatic cells and are predominantly of epithelial origin, e.g., prostate, breast, colon, urothelium and skin, followed by cancers originating from the hematopoetic lineage, e.g., leukemia and lymphoma, neuroectoderm, e.g., malignant gliomas, and soft tissue tumors, e.g., sarcomas.
Cancer Diagnostics and Prognostics
Microscopic evaluation of biopsy material from suspected tumors remains the golden standard for cancer diagnostics. To obtain a firm diagnosis, the tumor tissue is fixated in formalin, histo-processed and paraffin embedded. From the resulting paraffin block, tissue sections can be produced and stained using both histochemical, i.e., hematoxylin-eosin staining, and immunohistochemical (IHC) methods. The surgical specimen is then evaluated with pathology techniques, including gross and microscopic analysis. This analysis often forms the basis for assigning a specific diagnosis, i.e., classifying the tumor type and grading the degree of malignancy, of a tumor.
Malignant tumors can be categorized into several stages according to classification schemes specific for each cancer type. The most common classification system for solid tumors is the tumor-node-metastasis (TNM) staging system. The T stage describes the local extent of the primary tumor, i.e., how far the tumor has invaded and imposed growth into surrounding tissues, whereas the N stage and M stage describe how the tumor has developed metastases, with the N stage describing spread of tumor to lymph nodes and the M stage describing growth of tumor in other distant organs. Early stages include: T0-1, N0, M0, representing localized tumors with negative lymph nodes. More advanced stages include: T2-4, N0, M0, localized tumors with more widespread growth and T1-4, N1-3, M0, tumors that have metastasized to lymph nodes and T1-4, N1-3, M1, tumors with a metastasis detected in a distant organ. Staging of tumors is often based on several forms of examination, including surgical, radiological and histopathological analyses. In addition to staging, for most tumor types there is also a classification system to grade the level of malignancy. The grading systems rely on morphological assessment of a tumor tissue sample and are based on the microscopic features found in a given tumor. These grading systems may be based on the degree of differentiation, proliferation and atypical appearance of the tumor cells. Examples of generally employed grading systems include Gleason grading for prostatic carcinomas and the Nottingham Histological Grade (NHG) grading for breast carcinomas.
Accurate staging and grading is often crucial for a correct diagnosis and may provide an instrument to predict a prognosis. The diagnostic and prognostic information for a specific tumor is taken into account when an adequate therapeutic strategy for a given cancer patient is determined.
A commonly used method, in addition to histochemical staining of tissue sections, to obtain more information regarding a tumor is immunohistochemical staining. IHC allows for the detection of protein expression patterns in tissues and cells using specific antibodies. The use of IHC in clinical diagnostics allows for the detection of immunoreactivity in different cell populations, in addition to the information regarding tissue architecture and cellular morphology that is assessed from the histochemically stained tumor tissue section. IHC can be involved in supporting the accurate diagnosis, including staging and grading, of a primary tumor as well as in the diagnostics of metastases of unknown origin. The most commonly used antibodies in clinical practice today include antibodies against cell type “specific” proteins, e.g., PSA (prostate), MelanA (melanocytes) and Thyroglobulin (thyroid gland), and antibodies recognizing intermediate filaments (epithelial, mesenchymal, glial), cluster of differentiation (CD) antigens (hematopoetic, sub-classification of lympoid cells) and markers of malignant potential, e.g., Ki67 (proliferation), p53 (commonly mutated tumor suppressor gene) and HER-2 (growth factor receptor).
Aside from IHC, the use of in situ hybridization for detecting gene amplification and gene sequencing for mutation analysis are evolving technologies within cancer diagnostics. In addition, global analysis of transcripts, proteins or metabolites adds relevant information. However, most of these analyses still represent basic research and have yet to be evaluated and standardized for the use in clinical medicine.
Bladder Cancer
World wide, bladder cancer is the ninth most common form of cancer. Bladder cancer is more common in men than in women; of a total of approximately 336 000 new cases yearly, about 260 000 occur in men and about 76 000 in women. The incidence varies widely between countries, and also the type of cancer. In the industrialized world, the most common type of bladder cancer is urothelial carcinoma (appr. 90% of cases). In developing countries, squamous cell carcinomas are most common, although this type only contributes to a few percent of bladder cancers in the western world. The world wide incidence of urothelial cancer is approximately 3.3% of all new cancers, and nearly 150 000 deaths per year can be contributed to this disease. The risk of developing bladder cancer increases with age and the median age at diagnosis is 70 years for men and women combined.
Today, the largest known risk factor for bladder cancer is use of tobacco, particularly cigarette smoking. Other risk factors include flue gases from coal combustion and ionizing radiation. Genetic factors that contribute to the disease have as yet not been identified.
Bladder Cancer Diagnostics
Screening of patients for early detection of bladder cancer is generally not recommended today. A few markers have been approved by the FDA for use in urine screening, such as BTA-Stat and NMP22, however, these have not proven to be reliable enough. Blood in the urine is a common first symptom of bladder cancer, but is not always present. Other symptoms may be pain across the pubic bone, frequent urination and stinging, or symptoms similar to an ordinary bladder infection. When a patient presents with symptoms that may indicate bladder cancer, a CT-urography is performed. After the CT-urography, a cystoscopic examination is made in which a flexible tube is introduced into the bladder through the urethra. The tube is bearing a camera and a tool to remove tissue from dubious lesions. If tumor tissue is found, resection of the bladder is performed to remove all traces of tumor, and multiple biopsies are also normally taken from the mucous membrane, in a so called mapping procedure.
The cytological diagnosis of grade 1 tumors may be difficult, and the diagnostic accuracy is only about 50% in these cases today. Confounding factors may include e.g. inflammation.
Treatment of Bladder Cancer
Early detection and surgery with excision of the tumor may be of critical importance for a successful treatment. Superficial tumors can be surgically removed or “shaved off”, but for invasive tumors, more radical surgery may be needed, whereby the standard approach today is radical cystectomy/removal of the bladder, with or without chemotherapy. Bladder cancer typically metastasizes to regional lymph nodes, but distant metastases in the lung, skin, liver and bones are not unusual.
At the time of diagnosis, usually a transurethral resection of the bladder (TUR-B) is performed, which may in itself be a curative treatment for non-invasive bladder cancer. However, in cases with a high risk of recurrence, patients may be given chemotherapy or Bacillus Calmette-Guerin (BCG) as instillation treatment. In cases with multifocal tumors or frequent recurrences, intravesical instillation during a longer time period may be considered.
Cancer in situ of the bladder is currently treated by BCG instillation. If the tumor fails to respond to treatment, a cystectomy may be performed where all or part of the bladder is removed.
Muscle-invasive bladder cancer, stage T2-T4a, is currently treated by radical cystectomy and lymph node dissection of the small pelvis. Neoadjuvant chemotherapy can also be considered. According to current protocols in Sweden, adjuvant chemotherapy after cystectomy is only recommended to patients enrolled in controlled clinical trials. For inoperable patients, radiation treatment may be given, possibly in combination with chemotherapy.
Prognostics and Treatment Predictive Factors
Prognostic information can be obtained from tumor grade. Urothelial tumors are divided into five grades according to WHO standards: Papillomas, LMP (low malignant potential), and cancer grade 1-3. This grading is based on histological criteria and cell morphology. In grade 1, the tumor cells are well differentiated and grow mainly organized, in grade 2, the tumor cells are moderately differentiated and have a mainly unorganized structure, and in grade 3, the tumor cells are poorly differentiated.
Urothelial tumors are classified according to the TNM staging system. TIS represents tumor (or cancer) in situ. Cancer in situ of the bladder is a flat, low differentiated tumor (grade 3) that occurs in three different forms:
Primary: TIS without other tumor growth present;
Secondary: TIS discovered during follow-up after treatment of an exophytic tumor; or
Concomitant: TIS with other tumor growth present.
Stage Ta is a non-invasive tumor, and in the T1-stage, the tumor has invaded the lamina propria (the subepithelial connective tissue). In stage T2, the tumor invades muscle, in stage T3, the tumor invades perivesical tissue, and in stage T4, the tumor invades other organs.
Approximately 70% of bladder cancers are either entirely superficial tumors or only invading as far as the lamina propria (stage Ta or T1). Local recurrence of these tumors are common (50-70% recurrence rate), and patients normally need to be followed regularly with cystoscopic examinations to detect any recurrences at an early stage. This is a costly procedure causing great discomfort for the patient. These superficial tumors seldom progress to a more aggressive form, but in about 10-15% of cases they do. Among these tumors, three risk groups have been suggested by the European Association of Urology (EAU), namely:
Low risk tumors: Those that are LMP, or stage Ta and grade 1, or less than 3 cm in size;
Medium risk tumors: stage Ta tumors of grade 1 or 2 more than 3 cm in size; and
High risk tumors: tumors of stage Ta and grade 3, stage T1, or Tis.
The high risk tumors have an increased tendency to progress to more aggressive forms, and patients with high risk tumors will have to be closer monitored than those with low or medium risk tumors.
The least malignant tumors, Ta and T1, are associated with a relatively favorable outcome, and a current five-year survival rate of 90 and 75%, respectively. More invasive tumors have a less favorable prognosis with a five-year survival rate of approximately 60% for stage T2 and 35% for stage T3. Tumors with metastases (N1-4 and/or M1) have an even worse prognosis.
Cisplatin-based chemotherapy has proven to be efficient in advanced bladder cancer, with response rates of approx. 30% for single-agent treatment and more than 50% for combination treatment with other agents. However, long-term survival is currently low, only 10-15% of patients survive up to 5 years, and few molecular markers have proven to be of value in prediction of treatment response.